Ignition mixture



United States IGNITION MIXTURE Thomas J. Mulqueeny, Mathieson Chemical Virginia No Drawing. Application October 11, 1951, Serial No. 250,949

4 Claims. (Cl. 52-2 Godfrey, Ill, assignor to Olin Corporation, a corporation of Ignition compositions of the lead selenium type are well-known, and because of their gaslessness are desirable for use under certain circumstances, but because of their non-uniform performance, have not heretofore been adapted for other uses where uniformity of firing time is essential.

It has heretofore been burning of' such ignition composition by incorporating lead oxide (PbO) with it, and while the presence of lead oxide does lengthen the firing time of such mixes, the erratic performance is not thereby overcome. For example, with a series of identically loaded detonators in which the ignition composition consisted of 60% pure lead powder, 25% selenium, and 15% lead oxide (in which the lead oxide was incorporated as uniformly as possible by treatment of the mixture for several hours in a conical shaped, tumbling apparatus), the firing time:at one ampere varied from a minimum of 137 milliseconds to a maximum of 195 milliseconds, with an average of 173- milliseconds. This represents a variation above the minimum of 42.3%, which is considerably outside the range of variation which can be tolerated where firing time is an important factor.

The object of the present invention generally stated is to provide an ignition composition of the lead-selenium type in which the firing times are less erratic than has been previously experienced.

I have discovered that if in lieu of incorporating lead oxide as a separate ingredient with a lead-selenium mix, the particles of lead be deliberately and substantially oxidized so as to produce in situ thereon and retain thereon the desired quantity of lead oxide, the performance of the resultant mix time-wise is substantially improved. By substantially oxidized as expression is used herein and in the appended claims, it is intended to contradistinguish from the quick oxidation which lead particles undergo immediately upon exposure to air. To produce the desired quantity of oxide on the lead powder and to control the extent of the oxidation, it is preferred to heat the lead powder in an internally baflied rotating drum in an oxidizing atmosphere. The degree of oxidation varies with the temperature, time, particle size, and rate at which the drum is rotating. In general, the higher the temperature, the longer the time of treatment, the smaller the particle size; or the faster the rotation of the drum; the greater the oxidation. At a temperature of 250 C. three to four hours is required to produce an oxide content of about 20% on a charge of lead powder. The degree of oxidation desired depends upon the time characteristics which it is desired to achieve with the resultant mix. In general, the greater the oxidation of the lead particles, the longer the pulse-time and the firing time of the resultant mix.

As one example of an ignition mix prepared in accordproposed to control the rate of ance with the present invention, the lead powder was heated at a temperature of 250 C. and repeatedy sampled until it was oxidized, that is, so that the charge in the rotating drum consisted of four parts pure lead to each one part of lead oxide calculated as PbO.

This required four hours in a drum rotating at 22 R. P. M., l with lead powder having a finenesssuch that about 96% passed through a screen having 325 mesh pet-lineal inch. The oxidized leadv powder was then incorporated with selenium in the proportions of three parts of oxidized lead to each part of selenium, so as to secure a mix for v the purpose of comparison with a mix consisting of 60% pure lead powder, 25% selenium, and 15% lead oxide (separately introduced). The oxidation of the lead parprovide 10-40% of with the ignition mix (hereinafter designated mix B) wherein the lead oxide was formed in situ on the lead particles, were fired to compare their firing times. In both mix A and mix B, the ignition mixture contained lead powder, 25% selenium, and 15% lead oxide (formed in situ on the lead particles in the case of mix B). The results of the test are indicated in the following table: 1 4

' Total firing time [In milliseconds-at one ampere] Extreme i Variation Mix A; '17s a 13'; 195 .53 Mix B- 134 128 17 From the tabulated results, it is apparent that whereas with mixes in which the lead oxide is separately introduced, the maximum firing time was over 142% of the minimum firing time, with mixes wherein the oxide was formed in situ on the lead particles, the maximum firing time was only 113% of the minimum firing time. Thus the spread between maximum and minimum firing times is substantially reduced by producing the desired amount of oxide in situ on the lead particles.

The firing time of mixes containing oxidized lead is longer than the firing time for mixes which contain no oxide, but at comparable oxide contents, the mix in which the lead is oxidized has a consistently shorter firing time than comparable mixes in which the lead oxide is separately introduced. In order to reduce the firing time of a given mix, therefore, it is possible either to utilize lead with less oxidation, or to blend with lead of a given oxidation, lead of lesser or no oxidation.

To illustrate the effect of varying the degree of oxidation of the lead particles upon the pulse time for ignition mixes of the lead-selenium type, a series of tests comparing ignition mixes containing 27.6% selenium,

balance oxidized lead particles, were run, with the following typical results:

Pulse time [In milliseconds-at one ampere] Percent PbO Ave Max Min.

3.5 4.4 1.2 4.0 5.2 as i. 1 6.0 4.0 4.6 6.0 4.4

Patented Apr. 3,1956

iictates that the) lead particle's .in.' the. should notibe eater immanent-40% 1. Indeed," t isilpl qi nred'jthat. ignition mixeslpigeparediili aceerd-l oxidized to an extent e i h E t nt. .inventie .heye tthejlleau particles, herein ii i 4 mnennnet more ,tlianl20,%; 'fthu s, o g; substauti'atficton. offlsafety infthe per d m c of the detonators. a v a While, scientific. explanation for the improvement in the unifdrmityoflfir'ing times accomplished by oxidizing the; lead particles .1 instead: of .I'incoi'porating lead oxide in the Jnix is. not yet; ascertained withscertainty, i it may be postulated ithatbthef-resultsarelattrihutable;1to.the..uni-

Eormit'y in whichlhe lead iox deris distributed. with. refer enceQt'o'vthe leadv particles ,-throughout .the mixv, Since;

eacht,.particlellof.ipure glead may beiconsidered aS.-,being' coated..with 1ead;oxide,; and since .the depth :of thescoating.

amazes,

wilt-Q be; uniform .on. all par-ticles; which have ;;been; sub-i iected to the-same; oxidationltreatmenta it (is; apparent: that i all increments of lead carry equivalent increments of leads oxide. Thus in the mixing operation it is unnecessary to distribute three ingredients uniformly each with respect to two others,-butonly one ingredient, the selenium, need-be distributed'uniformly with'respect to one other, the oxidized lead particles,

From the foregoingdescription, those skilled in the art should readily understandlthe ;principles of the present,

invention, and realize that it accomplishes'its vobject',.and.i-

substantially l eliminates .-the erratic l performance. firingtime-wise of lead-selenium ignition mixes While the in; vention has been'de'scrib'ed with particular reference to a typical lead-selenium priming mix in which the selenium content amounted to 25%, it is to be understood that the invention is not limited to that particular proportion of selenium, but'that the invention is applicable to such ignition mixtures containing as much as 60% or as little as 15% selenium. l

Having thus described the, invention, whats-is claimed-r and desired ,to be securedby LettersPatent is:=

1. In the manufacture of lead-selenium ignitiom-mi tures, the improvement which comprises, providing particles of lead; and'substantiallyxbutincompletely oxidizing the lead particles before" incorporation with the selenium, to an extent,sufiicient toqprqvide 10-40% of lead oxide in the mix.

2. In a lead-selenium ignition mix, the improvement whi h ornpris the lead articles;-beingsub an ially b in o p t y o ized to an. ex ent suflicientt qiprow i vide, 10-40% lead oxidein athe mix. 1.

3." In a lead-.selenium. vignition rmix, the: improvement 7 which comprises,.,.the -v particles @of dead? being-i substang tiallyz uniformly v coated; withwsleadioxide sto provide: 10-40% of leadloxide in the mix said :particlehatiflgi cores, offunoxidized lead 4. An ignitionimix somprising ,paigticlteseof t:lead,;,said i;, particle's being substantially but incompletely oxidize to an extent;sufficient to provide 10T40%,-,o .lead oxide; in the mix. .and the, oxide. remaining in situ thereon References Cited in the filejaof, this patent UNITED, STATES PATENTS f QIHER.,-REEERENCES Goetzel: Treatise on Powder: Metallurgyf Vol. If'pub lished.i (l949t):iby:Inter-Science Publishers, Inc;, New York; London, :page 265. 

1. IN THE MANUFACTURE OF LEAD-SELENIUM IGNITION MIXTURES, THE IMPROVEMENT WHICH COMPRISES, PROVIDING PARTICLES OF LEAD, AND SUBSTANTIALLY BUT INCOMPLETELY OXIDIZING THE LEAD PARTICLES BEFORE INCORPORATION WITH THE SELENIUM, TO AN EXTENT SUFFICIENT TO PROVIDE 10-40% OF LEAD OXIDE IN THE MIX.
 4. AN IGNITION MIX COMPRISING PARTICLES OF LEAD, SAID PRATICLES BEING SUBSTANTIALLY BUT INCOMPLETELY OXIDIZED TO AN EXTENT SUFFICIENT TO PROVIDE 10-40% OF LEAD OXIDE IN THE MIX AND THE OXIDE REMAINING IN SITU THEREON. 